Interleukin 2 (IL-2) was first growth factor described for T cells. Since its discovery it was observed its ability to promote proliferation and survival of T in vitro cells (Smith, K A. (1988) Science. 240, 1169-76), as well as to boost immune response in the context of T viral infections (Blattman, J N, et al. (2003) Nat Med 9, 540-7) or vaccines (Fishman, M., et al. (2008) J Immunother. 31, 72-80, Kudo-Saito, C., et al. (2007) Cancer Immunol Immunother. 56, 1897-910; Lin, C T., et al. (2007) Immunol Lett. 114, 86-93). However, this classical role of IL-2 as a promoter of T immune response has been questioned recently by numerous experimental data (Almeida, A R., et al. (2002) J Immunol. 169, 4850-60; de la Rosa, M., et al. (2004) Eur J Immunol. 34, 2480-8, Malek; T R, et al. (2004) Nat Rev Immunol. 4, 665-74) showing that this cytokine is an homeostatic growth factor for natural regulatory T cells CD4+CD25+FoxP3+ (Tregs). Interleukin-2 has also been proposed as a major player in the mechanism by which regulatory T cells suppress the activity and expansion of other effector cells such as CD4 T helper cells, cytotoxic CD8 T cells and natural killer (NK) cells. In particular it has been recently proposed that regulatory T cells suppress other T cells, inducing the local decrease in the levels of IL-2 (Pandiyan, P., et al. (2007) Nat Immunol. 8, 1353-1362). This suppressive effect is based on: a) their ability to directly inhibit that effector T cells produce new IL-2 (Almeida, A R., et al. (2002) J Immunol. 169, 4850-60; Takahashi, T., et al. (1998) Int Immunol. 10, 1969-80; Thornton, A M., et al. (1998) J Exp Med 188, 287-96; Wolf, M., et al. (2001) Eur J Immunol. 31, 1637-45); b) their ability to sequester, internalize and degrade quickly the IL-2 present in their microenvironment (Pandiyan, P., et al. (2007) Nat Immunol. 8, 1353-62) and c) its ability to over-express the alpha chain of the IL-2 receptor (Kuniyasu, Y., et al. (2000) Int Immunol. 12, 1145-1155), which allows for a more efficient use of IL-2 when its concentrations are low.
In summary, IL-2 is a highly pleiotropic cytokine which is very relevant in the biological activity of different cell populations. This property makes the IL-2 an important node in the regulation of the immune response, making it an attractive target for therapies and complex immune modulation.
IL-2 has been used for several years in cancer therapy. In particular its use at high doses is an approved therapy in several countries for the treatment of metastatic melanoma and renal cell carcinoma. However, the direct use of IL-2 in patients is severely limited by its toxic effects and low efficacy. So much so that only 20% of eligible patients receive IL-2 based therapy and only 17% of those patients treated show an objective response. A likely explanation for this dramatic failure in the clinic setting is that therapy with native IL-2 also stimulates populations of regulatory T cells (Ahmadzadeh, M., et al. (2006) Blood. 107, 2409-14) which dampen the desired immuno-stimulation. Nowadays large amounts of pre-clinical evidence support this idea. In particular, experiments in murine models show that the primary activity of the IL-2 injected in vivo is the homeostatic expansion of natural regulatory T cells. Several strategies have been developed to mitigate the toxic effects of IL-2 therapy. Some of these strategies are based on the use of mutated variants of IL-2, designed to increase the capacity of this molecule to signal mainly by the high affinity receptor (alpha, beta and gamma chains) and not by the intermediate affinity receptor (beta and gamma chains). The basic idea is to promote signaling in T cells instead of signaling in NK cells, which are believed to be responsible for the observed toxic effects. The following inventions are in this line of work: U.S. Pat. No. 7,186,804, U.S. Pat. No. 7,105,653, U.S. Pat. No. 6,955,807, U.S. Pat. No. 5,229,109, U.S. Patent Application 20050142106. It is important to note that none of these inventions relates to muteins of IL-2 that have greater therapeutic efficacy than the in vivo native IL-2, based on their decreased ability to stimulate natural regulatory T cells.
Other mutated variants of IL-2 have been created with the aim of increasing their pharmacological activity by, for example, improving its folding or increasing their lifetime in blood. Among others, the following inventions are in this line of work: U.S. Pat. No. 4,959,314, U.S. Pat. No. 5,116,943, U.S. Pat. No. 4,853,332. Again, none of these muteins have a decreased ability to activate regulatory T cells or shows greater therapeutic efficacy.
Finally, it should be mentioned that in the literature there are numerous proposals of therapeutic agents (Kreitman, R. J. (2009) Curr Pharm Des. 15, 2652-64; Litzinger, M. T., Fernando, R., Curiel, T. J., Grosenbach, D. W., Schlom, J. and Palena, C. (2007) Blood. 110, 3192-201; Morse, M. A., Hobeika, A. C., Osada, T., Serra, D., Niedzwiecki, D., Lyerly, H. K. and Clay, T. M. (2008) Blood. 112, 610-8; Onizuka, S., Tawara, I., Shimizu, J., Sakaguchi, S., Fujita, T. and Nakayama, E. (1999) Cancer Res. 59, 3128-33; Quezada, S. A., Peggs, K. S., Curran, M. A. and Allison, J. P. (2006) J Clin Invest. 116, 1935-45) that propose to modulate or reduce the activity of regulatory cells vivo. These therapeutic agents have been tested in animal models or even in patients as a direct therapy of cancer or to enhance the effect of vaccines. There are also some reports that propose to modulate the activity of IL-2, in particular monoclonal antibodies (Boyman, O., Kovar, M., Rubinstein, M. P., Surh, C. D. and Sprent, J. (2006) Science. 311, 1924-1927; Boyman, O., et al. (2006) Expert Opin Biol Ther. 6, 1323-31; Kamimura, D., et al. (2006) J Immunol. 177, 306-14; Murakami, M., Sakamoto, A., Bender, J., Kappler, J. and Marrack, P. (2002) Proc Natl Acad Sci USA. 99, 8832-7; Tomala, J., Chmelova, H., Mrkvan, T., Rihova, B. and Kovar, M. (2009) J Immunol. 183, 4904-4912), to promote better or more effective immune responses. However, to our knowledge, there is no report in the literature, based on mutated variants of IL-2, showing the possibility of obtaining greater therapeutic efficacy based on their decreased ability to stimulate natural regulatory T cells.